Symptoms
Symptoms of bakanae disease first appear around a month after planting. Infected seedlings appear to be taller, slenderer, and slightly chlorotic compared to healthy seedlings. The rapid elongation of infected plants is caused by the pathogen's production of the plant hormone gibberellin. Plants with bakanae disease are often visible arching above healthy rice plants, with infected plants senescing early and eventually dying before reaching maturity. If infected plants do survive to heading, they produce mostly empty panicles.
Comments on the Disease
Bakanae is one of the oldest known diseases of rice in Asia but was first observed in California rice in 1999 and now occurs in all California rice-growing regions.
As diseased plants senesce and die, mycelium of the fungus may emerge from the nodes and may be visible above the water level. As plants mature and the water is drained, the fungus sporulates profusely on the stems of diseased plants. Sporulation appears as a pinkish, cottony mass and often contaminates healthy seed during harvest. The bakanae pathogen overwinters as spores on the coat of infested seeds but can also overwinter in the soil and on plant residue. Infected seed is considered the most important source of initial inoculum in California.
Management
The most effective means of controlling this disease is to avoid using seed that is infected with the pathogen. Seed treatment with a registered sodium hypochlorite product is effective at reducing the incidence of this disease and may be performed at either 3,000 or 1,500 parts per million (ppm) available chlorine.
For a 3,000 parts per million available chlorine solution:
- Prepare 3,000 ppm solution of sodium hypochlorite by adding a concentrated sodium hypochlorite product to the soak water. Make sure to use the product and water volumes indicated on the label. Thoroughly mix the dilute solution. Do not add concentrated sodium hypochlorite directly to seed.
- Check the concentration of the dilute solution to make sure it is at 3,000 ppm available chlorine.
- Soak rice seed in the dilute solution for 2 hours.
- Drain the dilute solution and replace with fresh water.
- Continue soaking and draining as usual (for at least 22 hours).
- Sow seed within 12 to 24 hours of draining. Fungal inoculum may increase exponentially on seed held in trailers longer than 24 hours after draining. If seed will be held longer than 24 hours, hold in water rather than draining to prevent the increase in inoculum.
For a 1,500 parts per million available chlorine solution:
- Prepare 1,500 ppm solution of sodium hypochlorite by adding a concentrated sodium hypochlorite product to the soak water. Make sure to use the product and water volumes indicated on the label. Thoroughly mix the dilute solution. Do not add concentrated sodium hypochlorite directly to seed.
- Check the concentration of the dilute solution to make sure it is at 1,500 ppm available chlorine.
- Soak rice seed in the dilute solution for at least 24 hours. No rinse is required before sowing.
- Sow seed within 12 to 24 hours of draining. Fungal inoculum may increase exponentially on seed held in trailers longer than 24 hours after draining. If seed will be held longer than 24 hours, hold in water rather than draining to prevent the increase in inoculum.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide’s properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| A. | SODIUM HYPOCHLORITE | 3,000 ppm or 1,500 ppm available chlorine | ||
| (Clorox Commercial Solutions Clorox Germicidal Bleach— 8.25% Sodium Hypochlorite): 3,000 ppm treatment | 4 gal product per 96 gal water for 2 hours | NA | NA | |
| Or | ||||
| (Clorox Commercial Solutions Clorox Germicidal Bleach— 8.25% Sodium Hypochlorite): 1,500 ppm treatment | 2 gal product per 98 gal water for 24 hours | NA | NA | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): NA | ||||
| COMMENTS: Preplant rice seed treatment. Do not apply undiluted product directly to seed. Drain and sow seed within 12 to 24 hours of draining, as fungal inoculum may increase exponentially on seed held in trailers longer than 24 hours after draining. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with different group numbers are suitable to alternate in a resistance management program. In California, make no more than one application of a fungicide with a mode-of-action group number associated with high resistance risk before rotating to a fungicide with a different mode-of-action group number; for other fungicides, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number. |
| NA | Not applicable |